The present invention related to a paper coloring apparatus for especially water colors or water-based inks.
Today, coloring paper in the form of a running web with water-based inks is effected by means of various kinds of coloring or painting apparatus and/or printing processes.
The main disadvantage of methods of today is that relatively large amounts of ink (more than 1,5 grams/m.sup.2) are transferred to the paper web. As water well may constitute 90% of the ink, this will lead to a relatively large water supply to the paper, involving a swelling of the paper fibers; the physical properties (dimensional stability, rigidness, etc.) of the paper getting lost or being substantially deteriorated. In order to stabilize the paper again subsequent to such conventional coloring, it is necessary to after-dry it by means of suitable equipment (hot air blowing, radiation using infrared rays, microwave-treatment, etc.). Usually, this is expensive, space-demanding and complex.
In a known coloring apparatus of the kind concerned, a color roller rotates partly submerged into a color basin, and cooperates with an overlying intermediate roller to which the color roller transfers coloring matter. On its part, the intermediate roller transfers coloring matter supplied thereto to an overlying inking-up roller which is adapted to transfer coloring matter supplied thereto to a running paper web. These three rollers have mutually parallel rotation axes.
It has been found that the adjustment of the relative positions of the rollers and pressure against each other greatly influence the amount of color transferred between the rollers. A weak pressure from a roller gives another transferred color amount than a hard roller pressure. Therefore, it is important that the pressure is constant along the line of contact between the rollers, in order to achieve an even color transfer laterally of the paper web.
In today's methods, the roller positions are usually adjusted by means of mechanical and/or electrical mechanisms, requiring much time and high professional capability. Usually, the adjustments have also to be tested out in order to control them.
As the roller pressure influences the transferred amount of color, it will also influence the amount of water transferred between the rollers when using water colors. This can lead to great problems adhering to the adjustment of the drying equipment, so that the paper subsequent to drying receives the correct conditioning (water content).
Mechanical adjustment of rollers as well as controlling their relative rotation speeds by means of either fixed gear transmissions or electric motors of their own require more energy for operation than the paper web is capable of supplying without allowing the paper tension to increase too much. Therefore, these roller systems require energy supply in order to operate. This supply of energy is usually taken from the main motor for the machine on which the paper coloring apparatus is mounted. Usually, such a coupling makes it more complex and expensive to find a suitable positioning of the paper coloring apparatus at already existing production machines.